1. Field of the Invention
The present invention is generally in the field of semiconductor devices. More particularly, the invention relates to fabrication of resistors in semiconductor devices.
2. Background Art
Many circuits fabricated using CMOS processes require a resistor. It is advantageous to use a CMOS process to fabricate a resistor on a substrate with other components of a circuit as an integrated circuit (IC). A polysilicon (poly) resistor can commonly be fabricated on a substrate with other components of a circuit in a CMOS process. It may be desirable to adjust a resistance of the resistor in the circuit. One example is in a radio frequency (RF) analog circuit, where the resistor may receive a signal as an input to an amplifier. If the resistor remains highly conductive when the signal is off, substantial crosstalk and noise can be introduced into the circuit. However, if the resistor is a poly resistor, its resistance cannot be adjusted and the resistor remains highly conductive. Furthermore, disconnecting the poly resistor would require an additional circuit.
A planar gate transistor may be used as a resistor where a voltage applied to a gate of the planar gate transistor is used to adjust its resistance. However, among other disadvantages, as the voltage changes, the resistance of the resistor would change in a highly non-linear manner. Thus, it would be difficult to control the resistance of the resistor. Furthermore, the amount of adjustment that could be made to the resistance would be limited. For example, a channel of the planar gate transistor would be inverted at a certain point well before it could be completely depleted. As such, using a planar gate transistor as a resistor cannot, for example, adequately prevent or reduce crosstalk and noise in a circuit.
It would be desirable to provide for a resistor that has an adjustable resistance and that can be fabricated using a CMOS process, while overcoming drawbacks and deficiencies of the art.